The instant invention deals in the art of braking systems and more particularly with braking systems for aircraft. Heretofore, it has been known to utilize a plurality of brake disks, alternately splined to the axels and hubs of aircraft wheels, to effectuate a braking effort on the wheels. While brake disks have been quite satisfactory for their heat dissipating characteristics, it has been found that the same wear and, hence, adjustments need to be made such that brake pedal travel and force are substantially consistent with braking effort irrespective of the wear experienced by the brake disk stack. Adjustment is also required such that a maximum amount of usage may be obtained from the brake disks.
Numerous approaches have been taken in the art to achieve the desired brake adjustment. It has been known to use different standard types of adjusters wherein brake adjustment is achieved by a frictionally slidable unit on a tube. Using the standard brake adjuster mechanism, it has been found that a wide variance of loads exist for any given distance of brake travel or brake application. In other words, the force versus displacement curves of the present standard types of adjusters do not trace each other on successive brake applications and as the brake disks wear. The force necessary to overcome the frictional engagement varies with each brake application.
Another shortcoming in utilizing the standard brake adjusters of the prior art is that design considerations must be given to the difference between static and dynamic coefficients of friction. When brake pressure is first applied, the first amount of travel experienced by the return mechanism is that known in the art as the "built-in clearance." The next portion of travel is that compensating for brake wear experienced during prior braking efforts. Above this, the force applied is that known as the effective brake force. However, with the static coefficient of friction being greater than the dynamic coefficient of friction, the force applied to effectuate movement of the standard adjuster to compensate for brake wear must be sufficient to overcome both coefficients of friction and the return spring brake on force. Should the standard unit slip, the spring follower may then return to a point where there is no longer a "built-in clearance." The brakes will then either stay in a locked position or, at best, there will be a loss of built-in clearance for subsequent brake applications.
Numerous approaches have been taken to circumvent the problems inherent with the present standard types of adjusters. Teachings of such approaches may be found in U.S. Pat. Nos. 3,376,959; 3,958,670; and 3,990,547. Applicant's own U.S. Pat. No., 3,926,283, shows yet another approach. While these patents teach an advancement over the standard apparatus, they themselves have certain drawbacks inherent therewith. For instance, applicant's own patent has an adjustability which is not infinitely variable, but which is limited by the spacing of the threads interengaging the various parts of the assembly. In certain of the other prior art, it is taught to draw a ball through a tube and thus expand the tube as brake wear compensation is made. The tube itself is characterized by a baked-on lubricant to reduce the frictional contact between the ball and the tube and thus reduce that portion of the adjustment load, thereby leaving only the load dissipated in the expansion process. In manufacture, the addition of the lubricant to the tube necessitates an extra step in manufacturing process. Further, once the ball has been drawn through the tube, it is not possible to reuse that adjustment mechanism in association with a new brake disk stack since the tube has been deformed.
With respect to the ball and tube type of brake adjuster, it has been found that the utilization of only the expansion load of the tube obviates the problem experienced in the standard unit transition between static and dynamic frictional forces as discussed hereinabove. It has further been found that such a brake adjuster operates satisfactorily and with a reasonable degree of predictability and repeatability. However, with such apparatus not being reusable and relying upon an expansion of a metal tube, requiring great force, it has become desirable to provide yet a better type of brake adjuster.